All aircraft (and occasionally other high speed vehicles), whether small general aviation aircraft or large airliners, have at least one pitot tube. Normally, a pitot tube extends from the airframe in various locations depending upon the particular aircraft configuration and range of speed. The pitot tube has an opening, generally circular, facing forward. The opening is exposed to ram air pressure while the aircraft is moving through the air. This ram air pressure is transmitted to an airspeed indicator in the aircraft or other vehicle instrument panel via air tubes. The aircraft's speed through the air can then be displayed for the pilot.
Knowledge of airspeed is very important to the pilot or operator of any high speed vehicle in order to ensure safe travel. When visibility is limited (as when flying in clouds where reference to instruments is necessary to conduct normal flight attitudes and navigation), if accurate airspeed is not available to the pilot, safe operation of the aircraft is highly unlikely.
Contamination of pitot tubes can occur from a number of other sources such as:
1. Moisture that does not drain from the tube when flying in rain or after the aircraft has been washed or has been exposed to blowing rain while on the ramp. PA1 2. Cleaning and/or polishing agents. PA1 3. Paint during a re-painting process on the aircraft. PA1 4. Insects or spiders that build nests within pitot tubes.
Moisture is generally not a problem because most pitot tubes have a drain hole that allows the automatic removal of moisture. Cleaning agents and paint generally are not a problem because the pitot tube is generally masked off during waxing and/or removed during painting, then returned to normal before flight.
Unfortunately, insects, spiders or other vermin enter and/or build nests within the pitot tubes thereby interfering with an accurate reading of the ram air pressure and, thus, the air speed. To prevent this, pitot tube covers are normally used for covering the pitot tube when the airplane is grounded or otherwise has no need for airspeed indication. Conventional types of pitot tube covers are often costly and complicated. Further, on occasion, they are forgotten and not removed prior to flight. When this happens the pilot is without knowledge of the air speed and is in a potentially dangerous situation. Such contamination can occur while the aircaraft is parked on a ramp or even in a hanger, causing obstruction and inaccurate airspeed indications.
Consequently, it is necessary that virtually all aircraft have a pitot tube cover in place to cover the inlet hole while the aircraft is not being flown. Pitot tube covers are available that can be slid over or strapped onto the pitot tube. There is a problem with conventional pitot tube covers, however. Despite having large visible RBF (Remove Before Flight), Flags attached numerous cases have been documented where pilots fail to remove the pitot tube cover prior to taking off, thereby contributing to a potential catastrophy. The conventional technology has addressed this problem in a number of ways.
U.S. Pat. No. 3,106,374, discloses an automatically releasable static discharge guard 10. This guard has a body 11 made of plastic rubber neoprene and includes a bore 17 for receiving the outer end 12 of a static discharge tube. The other end of the guard 10 is provided with a frusto-conical section 19 have an open end 21. In the event that the guard is left on the static discharge tube 13 during flight, the air stream entering opening 21 causes the guard to be detached from the static discharge tube 13.
U.S. Pat. No. 2,786,353 discloses a pitot tube cover for selective placement over a pitot tube 12. The cover includes a shell 18 having an end closure 20 and a funnel-shaped flange 22 at the forward end of the shell. The cover is made of plastic or metal, and is provided with a thin section or weakened ridges 24 which extends along the entire length of the cover. In the event that the cover is left on the pitot tube, the air stream entering the flange 22 causes the shell 18 to break apart at the ridges 24 and thereby fall off of the pitot tube.
U.S. Pat. No. 2,532,316 discloses an automatically releasable cover 2 for protecting a pitot tube 1. The releasable cover 2 as depicted in FIG. 3 and is made up of two L-shaped metal strips 4 and 41 fabricated of spring steel and which are stitched into the fabric 3. Two opposite latching studs or detents 6 and 61 are also provided so that, when the fabric 3 is folded over the pitot tube 1 as shown in FIG. 1, the spring steel metal strips 4 and 41 are retained together. A deflector 8 extends below the cover 2 and cooperates therewith in a manner whereby the air pressure against the deflector causes it to pivot and also causing the latching studs 6 and 61 to detach from one another thereby causing the cover 2 to fall from the pitot tube 1.
U.S. Pat. No. 2,488,810 discloses an automatic shutter mechanism for a pitot tube 2. The mechanism includes a shutter 6 attached to a shutter shaft 7 which extends through clamp bearing 13 and bears against the plunger spring 10. A wind pressure plane 12 is attached to the shaft 7. In operation, air being forced against the pressure plane 12 forces the pressure plane 12 along with shutter shaft 7 and shutter 6 rearwardly against the spring 10 thereby uncovering the opening 3 of pitot tube 2.
U.S. Pat. No. 5,026,001 discloses a pitot static tube cover 5 adapted to be received over an aircraft pitot tube 2. The cover is selectively mounted and dismounted by use of a long pole 24 and the holes 23 of crossbar 21.
U.S. Pat. No. Des. 351; U.S. Pat. No. Des. 337,0651; and, U.S. Pat. No. Des. 361,730 disclose pitot tube covers quite similar to that of U.S. Pat. No. 5,1026,001. Similarly, these covers require removal from the pitot tube by longitudinally sliding the cover on and off of the pitot tube.
Consequently, the conventional art does not meet the need for a safety pitot tube cover which will be automatically separated from the pitot tube once an aircraft, or other high speed vehicle reaches a predetermined speed. Such a cover must be light, simple and inexpensive so that it's loss in the air does not constitute an unreasonable expense. And must be of a material that upon ejection from the pitot tube during ground run, will not cause airframe damage.